1. Field of the Invention
The present invention relates to an optical switch for use in optical fiber communication and optical network technology, and particularly to an optical switch having a movable mirror to control the path of a light beam.
2. Description of Related Art
Optical signals are commonly transmitted in optical fibers, which provide efficient light channels through which the optical signals can pass. Recently, optical fibers have been used in various fields, including telecommunications, where light passing through an optical fiber is used to convey either digital or analog information. Efficient switching of optical signals between individual fibers is necessary in most optical processing systems or networks to achieve the desired routing of the signals.
A typical switch has one or more light input port(s) and at least two light output ports for performing switching or logical operations to optical signals in a light transmitting line/system or in an integrated optical circuit. Factors for assessing the capability of an optical switch include low insertion loss (IL less than 1 db), good isolation performance ( greater than 50 db), and fast switching speed (normally, tens of milliseconds).
Optical switches are divided into two types: a mechanical type and a non-mechanical type. In principle, the mechanical-type optical switches have a number of advantages over other forms of optical switches in applications where switching speed is not important. Mechanical-type optical switches offer lower insertion losses, low cross-talk, and insensitivity to wavelength of light.
Conventional mechanical-type optical switches come in two different designs: where the optical components move, and where the fibers move. Moving fiber switches involve the actual physical movement of one or more of the fibers to specific positions to accomplish the transmission of a beam of light from one fiber end to another under selected switching conditions. Moving optical component switches, on the other hand, include optical collimating lenses, which expand the beam of light from the fibers, and then, using moving prisms or mirrors, reswitch the expanded beam as required by the switching process.
The moving fiber switches have a stringent tolerance requirement for the amount and direction of fiber movement. The tolerance is typically a small portion of the fiber core diameter for two fibers to precisely collimate to reduce loss. The fibers themselves are quite thin and may be subject to breakage if not properly protected. On the other hand, reinforcing the fibers with stiff protective sheaths makes the fibers less flexible, increasing the force required to manipulate each fiber into alignment. Thus these moving fiber optical switches share a common problem of requiring high precision parts to obtain precise positioning control and low insertion loss. This results in high costs and complicates manufacture of the switches. Moreover, frequently moving fibers to and fro is apt to damage or even break the fibers. The switching speed of these moving fiber optical switches is also slow.
Conventional moving optical component switches have less stringent movement control tolerance requirements because of the collimating lenses.
One prior art moving optical component switch is illustrated in FIGS. 4, 5 and 6 and comprises a first and second light input ports 130, 150, a first and second light output ports 140, 160, and a movable reflecting element 170. The movable reflecting element 170 has two reflecting surfaces 171, 172, which are parallel to each other. The first reflecting surface 171 is movably arranged to reflect light from the first light input port 130 to the second light output port 160, and the second reflecting surface 172 is movably arranged to reflect light from the second light input port 150 to the first light output port 140.
The optical switch switches the light signals by moving the movable reflecting element 170 between two positions. In the first position, the movable reflecting element 170 is out of the path of the light beams and optical signals from the first input port 130 are transmitted to the first output port 140, while optical signals from the second input port 150 are transmitted to the second output port 160.
In the second position, the movable reflecting element 170 moves into the path of the light beams and the optical signals from the first input port 130 are reflected by the first reflecting surface 171 to the second output port 160, while the optical signals from the second input port 150 are reflected by the second reflecting surface 172 to the first output port 140.
If the first reflecting surface 171 and the second reflecting surface 172 were on the same plane, the optical switch would achieve low loss and precise collimation. However, the prior art device has the two reflecting surfaces or reflective films deposited on two opposite surfaces of a substrate having some thickness, so it is impossible for the first reflecting surface and the second reflecting surface to be on the same plane. Thus, as illustrated in FIG. 6, when the movable reflector moves into the path of the light beams, the optical signals from the second input port 150 and reflected from the second reflecting surface 172 may not exactly align with the first output port 140, as should the optical signals from the first input port 130 to the second output port 160. Consequently, a solution to the misalignment of the second light beam in this kind of optical switch is desired.
An object of the present invention is to eliminate the influence of a distance between two opposite reflecting surfaces of a movable two-sided reflecting element when such reflecting element is used to switch signals coming from a first and second input ports between first and second output ports in an optical switch.
An optical switch in accordance with one embodiment of the present invention comprises two input ports, two output ports and a switching element. The switching element includes a movable reflecting element and a fixed reflecting element. The movable reflecting element is a two-sided mirror and can move between a first position and a second position. The fixed reflecting element has at least one mirror, which is mounted parallel to the two-sided mirror. The first input port is aligned with the first output port, and the second input port is aligned with the second output port. When the movable reflecting element is out of the path of the light beams, the fixed reflecting element does not affect the path of the optical signals, and the optical signals from the first and second input ports are transmitted to the first and second output ports, respectively. When the movable reflecting element is moved into the path of the light beams, the fixed reflecting element functions to reflect the optical signals coming from the second input port so that they are reflected twice off the two-sided mirror, automatically accommodating the distance between the two reflecting surfaces of the moveable reflecting element and correctly aligning the reflected optical signals with the first output port. An efficient switching operation is thus achieved.
Other objects, advantages and novel features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.